Method of manufacturing adjustable voltage autotransformer



Sept. 22, 1970 L. A. KucHARsKl k3,529,348

METHOD OF MANUFACTURING ADJUSTABLE VOLTAGE AUTOTRANSFORMER Original Filed July l5, 1966 VENTOR 26 Loads A. KZqc/m/Sk N7 ,n BY l A I' 1 ,"'rqwf'll l mi Z5 Y 2.; 25 24 fram/sys United States Patent O 3,529,348 METHOD OF MANUFACTURING ADJUSTABLE VOLTAGE AUTOTRANSFORMER Louis A. Kucharski, Bristol, Conn., assignor to The Superior Electric Company, Bristol, Conn., a corporation of Connecticut Original application July 15, 1966, Ser. No. 565,633, now Patent No. 3,466,585, dated Sept. 9, 1969. Divided and this application Sept. 23, 1968, Ser. No. 798,224

Int. Cl. H011' 43/00 U.S. Cl. 29-597 5 Claims ABSTRACT OF THE DISCLOSURE A method of forming a commutating surface wherein wires are covered with an insulating plastic which is forced between the wires to expose same.

The present invention relates to an adjustable voltage autotransformer having a commutating surface on which a brush is relatively movable in electrical engagement therewith and more particularly to the commutating surface and the method of making thereof.

This is a division of application Ser. No. 565,633, filed July 15, 1966i now Pat. No. 3,466,585.

In U.S. patent application Ser. No. 300,246, tiled Aug. 6, 1963, now Pat. No. 3,293,582, by Clifford G. Schmitt and assigned to the assignee of the present invention, there is disclosed an adjustable voltage autotransformer having a commutating surface. The autotransformer includes a coil formed by winding a length of wire on a magnetic core and the commutating surface is formed by a flattened similar portion on each of most of the turns of the winding. The portions are positioned about the path of movement of an electrical conducting brush that is spring urged thereagainst. By altering the position of the brush on the commutating surface, the output voltage may be adjusted.

The similar portions of the turns and the lengths of the turns adjacent thereto on the coil are covered with a relatively thick hardened covering of epoxy material which serves to bind the similar portions together to decrease, among other factors, their inclination to physically move and thereby enable the autotransformer to handle more power than has heretofore been possible. Though such a covering has been found exceedingly satisfactory, the commutating surface was so formed as to be only minutely above the face of the epoxy coating between the portions and hence was quite subject to permitting foreign matter to become interposed between the brush and the commutating surface thereby creating the possibility of malfunctioning. Also the quantity of coating which remained on the coil after manufacturing processes subsequent to its depositing was inherently limited and only a fraction of the total deposited thus restricting the Structural binding between the turns in addition to increasing the costs thereof.

It is accordingly an object of the present invention to provide an adjustable voltage autotransformer having a commutating surface formed of conducting segments in which there is a relatively thick hardened epoxy covering deposited on the coil but yet in which the face of the epoxycovering in the interstices between the Segments is recessed below the commutating surface.

Another object of the present invention is to achieve the above object and simultaneously increase the quantity of hardened coating which lies in the interstices between the segments and at the end portions of the segments to thereby more securely bond the segments together and to the core.

Patented Sept. 22, 1970 A further object of the present invention is to provide an adjustable voltage autotransformer which achieves the above objects and which is more economical to manufacture by not only having less of the hardened covering applied to the coil but also less to be removed during the manufacturing process.

In carrying out the present invention, a feature thereof resides in providing a coil formed by winding a length of conducting wire on a closed core of magnetic material. In the specific embodiment shown, the core is annular and the `winding is toroidal and an arcuate commutating surface is formed on an end of the coil. At least this end of the coil is covered by a relatively thick hardened epoxy coating, such as may be deposited by heating the coil, exposing it to epoxy powder that upon engaging the heated coil melts and becomes attached thereto. Upon removal of the then coated coil from the powder and the cooling thereof, the melted powder hardens, becoming coherent and adherent and serving to bind the contacted parts together.

The present invention not only includes the above steps as disclosed in said copending application but also includes the step of pressing a resilient member against the portion of the coil where the commutating surface is formed whilethe covering is still in its semiliquid state and before it hardens. The pressing serves to displace the covering on the similar portions into the interstices between the segments thereby increasing the quantity of coating therein and also forces the excess coating on the similar portions radially from these portions to create thicker rims of covering about the ends of the portions.

During the pressing operation, the face of the covering in the interstices is caused to be recessed in most interstices below the level where the commutating surface is formed and thus will thereafter lie below said surface after it is formed. Naturally the distance which the face of the covering in the interstices lies below the level of the commutating surface depends upon many factors including wire size, width of the interstices, etc. However, though the face of the covering in the interstices is lower than in the above-noted application, the forcing of the material on the commutating surface into the interstices between the segments has been found to cause the coating to generally adhere to the core in the interstices, thereby generally decreasing the bond between the segments at the commutating surface but increasing the bond between the segments at the ends of the commutating segments with the net result being a bonding of the segments together at least as completely as disclosed in the abovenoted application. Moreover, the bond of the coating at the interstices to the core provides a restraint on the segments which opposes their tendency to raise above their normal position, thereby decreasing their tendency to so rise.

Other features and advantages will hereinafter appear.

In the drawing:

FIG. 1 is an elevation of an adjustable voltage autotransformer, partly in section, and in which the present invention is incorporated.

FIG. 2 is a plan taken on the line 2-2 thereof.

FIG. 3 is a section taken on the line 3 3 of FIG. 2 and enlarged to show details of construction.

FIG. 4 is a view similar to FIG. 3 showing sections of similar portions prior to the application of the coating.

FIG. 5 is a view similar to FIG. 4 with the covering having been applied but not being still in its semiliquid state.

FIG. 6 is a view similar to FIG. 5 (but inverted) showing the step of pressing the covering at the similar portions.

FIG. 7 is a view similar to FIG. 6 and in which the covering has become hardened.

ice,

FIG. 8 is a detail, somewhat enlarged, taken on the line 8 8 of FIG. 2.

FIG. 9 is a detail, somewhat enlarged, taken on the line 9`9 of FIG. 2.

FIG. 10 is a pictorial illustration of one manner of pressing the covering.

Referring to the drawing, the autotransformer is generally indicated by the reference numeral 10 and includes an annular core 11 formed by spirally winding a thin strip of magnetic metal. Positioned at the ends of the core are end caps 12 and 13 and a length of circular electrical conductor wire is wound thereover to form in the embodiment herein described a single layer of toroidal winding 14. The core 11, the winding 14 and the end caps 12 and 13 constitute, as hereinafter referred to, a coil and it is supported between a base member 15 and a clamping member 16. The members 15 and 16 also support a shaft 17 for rotational movement about the axis of the coil. The shaft 17 further carries a disk-shaped radiator 18 on which 1s supported a brush 19. Rotation of shaft 17 by a knob 20 or other means fast on the shaft 17 arcuately moves the brush 19 about the end of the coil.

The top end cap 12 is formed with an arcuate heightened portion 21 and a commutating surface, generally indicated by the reference numeral 22, is formed thereon, as will be hereinafter appreciated, by baring a similar portion il: of most, if not all, of the exterior turns of the winding Shown in FIG. 3 is an enlarged view of a chordal section taken lengthwise of the commutating surface 22 at the heighthened portion 21. The length of conducting wire that forms the winding 14 has an insulating covering and thus as shown in FIG. 4, after it is wound and pr1or to forming a commutating surface, each of the similai portions 23 has an insulation layer 24. The turns of the winding 14 are somewhat closely spaced but created between the similar portions are interstices 25 that extend transversely of the commutating surface.

In the forming of the commutating surface, a chordal section of each of the similar portions including the insulating layer is removed, as by grinding, to provide a face 26 of the conductor on each of the similar portions and a plating material 27 is applied thereto such that the upper face of the plating material of each similar portion constitutes the commutating surface 22 which is engaged by the brush.

As set forth in the above-mentioned copending application, there is deposited on the coil that includes the similar' portions 23 and the parts of each turn adjacent thereto a relatively thick hardened covering 28. The covering is epoxy material and is preferably deposited by heating the coil and exposing the same to a quantity of epoxy powder so that the heated coil melts the epoxy powder upon engagement therewith and the melted powder coalesces. The end of the coil where the commutating surface is to be formed is so coated for a length of one inch or so and thus the coating extends for such a length on both the inner and outer peripheries of the coil with the depositing being of a substantially constant thickness. In addition, as shown in FIG. 5, the semiliquid covering partially enters into the interstices 25 between the similar portions of the turns.

In accordance with the present invention, after the epoxy covering has been deposited and the coil is still hot with the covering being somewhat fluid, the end of the coil is then pressed against a at resilient sheet material with substantial force. The covering on the similar portions where they are raised by the heightened portion 21 is forced off of the similar portions so that the similar portions become substantially free of the covering. Shortly after the pressing operation has commenced and while the coil is still being pressed, a liquid bath 29 is caused to immerse the coil and sheet 30'. The bath is held in a container 29' and serves to cool the coil while the sheet 30 maintains pressure on it. It has been found that water at room temperature is a satisfactory material for the bath 29. The displaced covering, as shown in FIG. 6', is forced by the pressing operation into the interstices to substantially ll them and the remainder of the displaced covering is forced radially of the similar portions to form an inner rim 31 and an outer rim 32 of thicker coating material at the ends of the similar portions.

FIG. 7 depicts the similar portions and covering after the covering has hardened. The interstices 25 have become substantially lled with the covering and the upper face 33 of the covering in the interstices is generally about the midpoint of the similar portions. It will be understood that the relative position of the face' 33 depends on many factors including the resilience of the sheet material 30', the size of the conductor, the width of the interstices, the thickness of the semiliquid covering, the force with which the material 30 is pressed against the coil, etc. In autotransforrners with larger wire size and larger interstice, the face may lie below the midpoint of the similar portions while in the other autotransformers, the face may be somewhat higher. Also, even with the same autotransformer, the relative position of the face may vary vbetween interstices as the interstice width is generally not exactly constant. The present invention however desires to force the semiliquid covering olf the similar portions and to have the face 33 of the interstices lie below the yface 26 of the conductor.

After the covering 28 has hardened, as by being cured in a post-heat oven at curing temperatures, a chordal segment is then removed from each of the similar portions to create the flat face 26 of the conductor which lies above the midpoint of the conductor and also the insulation layer 24 is removed to provide a face 34 of the insulation layer. lhe plating material 27 is then applied to the face 26 and is preferably a metal such as silver, rhodium, gold or layers thereof which are inherently less oxidlzable than the copper face 26 of the conductor.

The tremoval of the chordal segment is preferably effected by grinding and a feature of the present invention resides in eliminating the necessity of grinding away a substantially thick hardened covering on the similar portions as the pressing step removes most, if not all, of the covering from the segments of the similar portions that are ground away.

As shown in FIG. l, the heightened portion 21 causes the similar portions to be raised somewhat above the remainder of the turns inwardly thereof at the end of the coil and the length 0f the turns outwardly of the similar portion are recessed below the heightened portion by the turns being bent over the edge of the coil. In the step of pressing, as described in connection with FIG. 6 the displacement of the quantity of covering on the simllar portion causes the material to form the rims 31 and 32. As shown in FIG. 8, the rim 32 is formed on the outer edge of the similar portions with this rim of covering being noticeably thicker than the covering on the side of the coil. Also, as shown in FIG. 9, on the inner portion the other rim 31 is formed with it also being noticeably thicker than the covering as initially deposited.

The sheet material 30 is supported by a rigid at plate (not shown) to enable the force to be applied to it throughout its area. One material from which the sheet may be formed is high temperature silicone rubber having relatively resilient characteristics.

In use, the current that passes between the brush 19 and the commutating surface and which includes both the output current and the short-circuited turn current may be of such a value `as to cause the brush and contacted segments of the commutating surface to become substantially hot. This in turn tends to cause the hot segments to raise upwardly away from the end cap and out of plane of the commutating surface. The segments, upon cooling, may not revert to their original position and thus if they remain out of the plane of the commutating surface they create an obstructon which is detrimental to the operation of the autotransformer as the brush has difficulty moving thereover.

The hardened covering as set forth in the above-mentioned copending application serves to bind all the segments of the turns together. If one or two segments are heated to a degree which does tend to raise them, the adjacent turns will also be caused to be raised by reason of their being bound together. Accordingly, rather than there being an abrupt inclination above the commutating surface caused by only one or two raised turns, there is in effect only a slight hill or gradual rise caused by many turns and which normally does not prevent operation of the autotransformer.

The present invention maintains at least the sarne effective bond between the similar portions by the thicker rims 31 and 32 at the ends of the segments providing mone bonding while the segments will have less by reason of the covering adhering to less of the segment above the midpoint of the wire. Moreover, the covering when forced into the interstices will suiciently fill most of the interstices so that adherence generally occurs with the surface of the end cap 12 thereby increasing the resistance of the segments to raising away from the end cap.

It will accordingly be aprpeciated that there has been disclosed an adjustable voltage autotransformer which is capable of handling at least as much power as the heretofore known similar sized autotransformers described in the above-noted application. This is achieved by the hardening covering not only bonding the segments to each other to restain their individual movement but also by bonding them to the core in the area where the commutating surface is formed. Thus the segments are held not only against individual movement with respect to each other but also with respect to the core. Moreover, the increased holding of the segments has been achieved with a reduction in the cost of manufacture thereof by reducing the amount of covering required and by eliminating removal of substantial portions from the segments when the commutating surface is formed.

Variations and modifications may be made within the scope of the claims and portions of the improvements may be used Without others.

I claim;

1. The method of forming a commutating surface having spaced conducting segments constituting a path corresponding to a course of movement of a conductive brush that rides thereon in electrical engagement therewith comprising the steps of forming a coil by winding a length of conducting wire on a core to form turns, a similar portion of at least a plurality of turns approximating said path with interstices being formed' between said portions, depositing a relatively thick liquid covering on and adjacent said similar portions, pressing at least the area of the said liquid covering at the portions to Substantially force said covering off of said portions and into the interstices between the portions to substantially ll most of said interstices, hardening said' covering to cause adherence thereof to said similar portions, removing to a surface somewhat approximating the commutating surface a part of the conductor from the similar portions to form an exposed face, said covering remaining in the interstices below the face, and bonding to the face a coducting material to form a conducting segment having an outer surface that forms the commutating surface.

2. The invention as defined in claim 1 in which the step of pressing consists of forcing a resilient member against the covering on said' portions.

3. The invention as defined in claim 1 in which the similiar portions are raised somewhat above the core and the step of pressing also includes forcing the semiliquid covering outwardly from the portions to form at least an outer rim.

4. The invention as defined in claim 1 in which the step of pressing includes forcing the liquid covering in most of the itersticcs below the surface to which the part of the conductor is removed from each similar portion.

S. The invention as dened in claim 1 in which the depositing includes the Steps of heating the coil, and coalescing epoxy powder thereon to form the covering and in which during at least part of the duration of the step of pressing at least the similar portions of the coil are immersed in a cooling bath to reduce the liquidness of the surface of the covering.

References Cited UNITED STATES PATENTS 2,668,894 2/ 1954 Coates 29-597 2,949,592 8/1960 Smiley 336-148 3,049,604 8/ 1962 Showalter 200-166 3,293,582 12/ 1966 Schmitt 336-149 JOHN F. CAMPBELL, Primary Examiner C. E. HALL, Assistant Examiner U.S. Cl. X.R. 

